The invention relates to a compact, water impermeable rubber material for use as expansion joints in roadways, sidewalks and similar structures. More particularly, it relates to a novel combination of concrete members and impermeable rubber material, which provides for an improved expansion joint compared with felt joint fillers, which are currently used.
In the construction of roads and sidewalks expansion joints are placed at regular intervals to compensate for the contraction and expansion of the material used as the pavement. In this manner discrete sections of roadway or sidewalk can expand and contract independently of each other without causing undue stress or cracks in the surface.
Typically, a felt strip is laid vertically at regular intervals between adjoining slabs to provide an expansion joint. However, there are many drawbacks to using a felt-like material. It should be pointed out that expansion joints generally create a problem in that they interrupt what would otherwise be a continuous top surface. These gaps can allow water to get beneath the surface which creates problems upon freezing due to expansion. Felt is a material comprised of wool, fur or hair, for example, which is compressed and heated to form a solid material. As can be appreciated, felt is not particularly weather resistant or water impermeable. As a result water can seep through a felt expansion joint and accumulate underneath the paving surface. This is particularly a problem during colder weather when sections of roadway or sidewalk would be most contracted resulting in larger gaps, in the area of the expansion joints, than would be present in warmer months. In addition, water, which permeates the expansion joint filler is likely to freeze during colder months.
In order to overcome some of these deficiencies, part of the felt expansion joint, which is visible between two slabs is removed. For example, the exposed felt is milled out approximately one half inch down. This creates a gap between slabs, which is then filled with a sealer, e.g. tar. This is an expensive and time-consuming process.
Various attempts have been made to provide an expansion joint material which overcomes these deficiencies. U.S. Pat. No. 1,280,572 issued to Spiegel on Oct. 1, 1918 describes an expansion joint for roads which comprises a resilient material having surface layers of non-resilient material adhesively fixed to it. Spiegel suggests the following as materials which can be used for his expansion joint. The resilient portion of the joint is a compound which consists of asphalt, sawdust, spent tan bark or like ingredients. Surrounding this core are two felt strips saturated with asphalt. An additional layer of asphalt with a high melting point is then applied. Finally, crushed stone is applied to the outer surface. The roughened outer surface is intended to readily adhere to the face of the adjacent road bed. in this manner it is hoped that gaps will not form between the expansion joint material and the roadway.
The Spiegel expansion joint has several drawbacks. First, it is not made of uniform material. The embodiment in FIG. 2 shows nine (9) layers of material. This has obvious disadvantages with regard to cost and complexity of manufacture. In addition, compound 1 includes organic materials which are not water impermeable. Felt strips 2, although including asphalt, are not totally waterproof.
U.S. Pat. No. 1,248,909 issued to Pullar on Dec. 4, 1917 discloses a bitumen product which can be used as an expansion joint. The material is made by incorporating a layer of woven or mesh fabric to the surfaces of a pure asphalt or bituminous compound. Pullar suggests using a fabric woven or formed with a mesh within the range of about 10 to about 200 openings per square inch. The mesh is applied to the bituminous material by mechanical pressing and then subjecting the surface to a heating process. The result is that the bituminous material flows through the openings of the fabric and forms an integrally connected thin bonding film on the outer surface of the fabric. Again, Pullar has the disadvantage that it is not of uniform composition.
Gage, U.S. Pat. No. 1,637,480 describes a device to prevent cracks from forming in the surface of a pavement where cracks reside in the underlying foundation. In Gage, strips of bituminous impregnated felts or fabrics can be laid across the existing openings to prevent surface paving material from working its way into the openings. This method allows movement of the underlying foundation in the vicinity of the crack without translation through movement in the paved surface. Although Gage solves the problem of movement in the underlying foundation, he does not provide for expansion in the top surface. Also, the method does not require these strips to be exposed. As a result, Gage offers a material which is water permeable and therefore not suitable for an exposed expansion joint.